Hint: Photosynthesis is a process in which green parts of the plant synthesize or manufacture complex organic food substances (carbohydrates) using carbon dioxide and water in the presence of sunlight and release oxygen as a by-product.
In the process of photosynthesis, energy from the sun is converted into chemical energy. It is an anabolic, endergonic (requiring energy) and oxide-reduction process. Sunlight plays a major role in our sustenance than we may expect, as all the food we eat and all the fossil fuels we use, they are all products or by-products of photosynthesis. Photosynthesis converts radiant energy into forms of energy that can be used by biological systems.
Now consider the above options:
A) Organic matter- The productivity of an ecosystem refers to the rate of production for the amount of organic matter that has accumulated per unit area in unit time. Gross Primary Productivity (GPP) is referred to as the total rate of photosynthesis including the organic matter used up in respiration during the measurement period.
B) Oxygen- It is released as a by-product during the process of photosynthesis, is a by-product it cannot be treated as the GPP of photosynthesis.
Hence, this option is not correct and void.
C) Carbon dioxide- It acts as an agent during the process of photosynthesis and helps in the making of organic matter. Hence, this option is incorrect.
D) Chlorophyll- Chlorophyll fluorescence tracks seasonal vibrations of photosynthesis from leaf to canopy in a temperate forest. Thus, this option is also incorrect.
Hence, GPP is the rate of production of organic matter.
Note: According to former estimates, only 10% of dry matter is produced by bland plants while 90% of it is formed in oceans.